Strut members have been used as integral components of vehicle suspension systems for quite some time. Examples of vehicle suspension struts are shown in the following patents: Hassan U.S. Pat. No. 4,804,169; McClellan U.S. Pat. No. 5,078,370; Weaver et al. U.S. Pat. No. 5,308,048; Perkins U.S. Pat. No. 5,228,717; Pacis U.S. Pat. No. 4,260,176; Perkins U.S. Pat. No. 5,145,204; Kakimoto U.S. Pat. No. 4,756,517; Taihou Kogyo, K K Japanese Patent Specification No. 58-88243(A) and Gee British Patent Specification No. 1,203,435.
McPherson type strut suspension systems typically include a suspension strut that comprises a tubular housing assembly having an outer casing, a cylindrical piston member received in the upper end of the housing and an exteriorly disposed helical suspension spring that surrounds a portion of the casing. The helical spring usually comprises the suspension spring for the vehicle. A mounting tower having a generally radially extending portion is provided for use as a seat by one end of the spring. A spring support member can be formed on the casing to support the lower end of the helical spring.
The strut is placed between a relatively fixed (sprung) portion of the vehicle, such as a body panel or frame member, and a movable (unsprung) portion of the vehicle such as a plate member or knuckle which ultimately attaches the strut to the vehicle wheel. In most strut suspension systems, the axially movable piston is connected to the body frame member, and the casing is attached to the unsprung member, such as the wheel.
One challenge faced by designers of suspension systems is to reduce the amount of space required for the suspension system. In this regard, car manufacturers have found that the consumers prefer vehicles having increased usable space, such as interior room and trunk room. If the space required by the suspension system can be reduced, the usable space within the vehicle can be increased.
To some extent, suspension system designers are constrained in their ability to reduce the size of the suspension system because of the function performed by the suspension system. For example, the strut must have a housing and piston that are sufficiently long enough to accommodate the vertical travel of the wheel as it moves up and down during vehicle travel. As such, the strut housing must be long enough to accommodate the full travel (stroke distance) of the piston between its fully collapsed position (i.e. that point when the piston is fully inserted within the interior of the housing) and its fully extended position (i.e. the position wherein the piston is fully extended to its maximum extent outside the housing).
Another functional constraint that affects the ability of the designer to reduce the length of the suspension strut (and hence reduce its size) is the radially directed, side loading forces that are exerted upon a strut. Although the predominant forces exerted upon a strut are those axially directed forces which are exerted by the vehicle wheel moving upwardly and downwardly, radially directed side loading forces are also exerted on the suspension strut. One source of such side loading forces is braking the vehicle.
It is important to be able to handle these side loading forces without reducing the ability of the strut's piston to slide within the cylinder of the strut housing. Additionally, by making a strut which is capable of handling higher side loading forces, the suspension designer has more flexibility to choose alternate suspension geometries, which although imposing greater side loading forces, requires less space.
In a typical suspension prior art strut housing, the upper (first) end of the housing includes an aperture for receiving the piston member. A bushing is placed adjacent to the aperture for slidably receiving the piston member. Because of the presence of bushing, the side loading forces that are exerted on the strut will tend to cause the piston member to pivot about a radially extending axis defined by the bushing at the first end of the housing. This pivoting action of the first end of the piston in a radial direction causes the second (lower) end of the piston member to move in an opposite radial direction. To deal with these side loading forces, strut designers typically employ a side load force absorbing member that is disposed near the second (lower) end of the piston. In most known struts, this side load force absorbing member consists of a bushing member. To prevent the lower bushing member from becoming pinched against the side of the housing interior, and thus being prevented from moving easily within the housing interior, a stop member is usually placed at a spaced relation from the bushing member. However, one difficulty encountered when increasing the space between the stop member and the bushing is that as the stop member defines the limit of travel of the piston, any increase in distance between the stop member and the bushing necessarily increases the length of the strut member.
It is therefore an object of the present invention is to provide a suspension strut which has a reduced overall length, when compared to prior art struts, but which still maintains the same travel distance as prior art struts.
It is a further object of at least one embodiment of the present invention to provide a suspension strut design which is more durable than known strut assemblies.
It is also an object of the present invention to provide a suspension strut that is capable of satisfactorily handling greater side loading forces without compromising the ability of the strut's piston to slide within the cylinder of the strut housing.
The capability of a strut to absorb greater side loading forces provides the suspension designer with a greater flexibility in the overall design of the suspension configuration, by allowing the designer more freedom in positioning the strut.
To understand why this occurs, it is useful to understand the nature of the forces that are exerted on the strut and suspension system.
Turning now to FIGS. 12-15, the geometric relationship between the various suspension components is shown schematically. FIGS. 12-14 show examples of suspension systems that can be achieved with the new, shorter strut of the present invention.
FIG. 12 shows a suspension system 400 where a tire/wheel combination 410 has an axis 412 about which it rotates, and an imaginary line 414 which is perpendicular both to the axis 412 and to the road surface 416 upon which tire 410 travels. A pair of lateral links (shown schematically as a single link) 418 have an inboard end 422 which is connected to a spring component of the vehicle body or frame, and an outboard end 420 that is connected to a knuckle (not shown) of the suspension assembly. The strut assembly 424 includes a piston-containing strut member 426 and a spring member 428 which exteriorly surrounds the strut member 426. In the embodiment shown in FIG. 12, the strut member 426 and spring 428 are disposed coaxially, so that both share a common centerline or axis 430. During operation of the suspension system 400, side loading forces are directed on the strut member 426 in a direction indicated generally by arrow F.sub.1. In the embodiment shown in FIG. 12, it will be noted that the outboard end 420 of the lateral link is disposed inboard of the centerline 430.
The suspension systems 500, 600 of FIGS. 13 and 14 represent the same type of components in a different suspension geometry. The components of FIGS. 13 and 14 include a tire and wheel assembly 510, 610, having an axis 512, 612, respectively, and an imaginary line 514, 614 that is perpendicular to the respective axes 512, 612 and the road surfaces 516, 616. Lateral link pairs 518, 618 have respective outboard ends 520, 620 and inboard ends 522, 622. The respective strut assemblies 524, 624 each include a piston containing strut member 526, 626 and a radially outwardly disposed spring member 528, 628. Each of the respective strut members 526, 626 has a centerline (axis) 530, 630. In the embodiment shown in FIG. 13, the spring 528 and strut member 526 are coaxial, and as such share a common centerline 530. In the embodiment shown in FIG. 14, the spring 628 and strut 626 are positioned at offset angles. As such, the centerline 630 of the strut member 626 is offset from and is different than the centerline (axis) 632 of the spring 628. It should also be noted that the outboard ends 520, 620 of the respective lateral link pairs 518, 618 are disposed relatively outboard of the respective center lines 530, 630 of the strut members. However, although the outboard ends 520 of link pair 518 are disposed outboard of the centerline 530 of spring 528 (FIG. 13), the outboard ends 620 of link pair 618 are disposed relatively inboard of the centerline 632 of offset spring 628.
The ramifications of these particular geometries are discussed below.
In the embodiment shown in FIG. 12, the center line 430 of the spring 428 is directed relatively outwardly of the outboard end 420 of the lateral link 418. This differs from the embodiment shown in FIG. 13 wherein the center line 530 of the spring 528 is disposed relatively inboard of the outboard end 520 of the lateral link 518. Because of this, the relative side loading force F.sub.1 that is directed against the strut 426 is relatively less than the side loading force F.sub.2 exerted against strut 526 of FIG. 13. Although the suspension geometry shown in FIG. 13 has a "size" advantage, when compared to that shown in FIG. 12, because of the reduced amount of space that it requires, it also has a drawback. In particular, since the side loading force F.sub.2 that is exerted on strut 526, is greater than the side loading force F.sub.1 directed on strut 426 (at FIG. 12), one desiring to use the suspension geometry shown in FIG. 13, would need to design a strut 526 that is capable of carrying more side loading force.
Present, prior art suspension systems are designed to reduce the side loading force F.sub.1 to a level that is within the load limits that existing struts are capable of handling, by utilizing a configuration similar to the one shown in FIG. 15. The suspension geometry shown in FIG. 15 helps to reduce side loading force by offsetting the center line 732 of the spring 728 from the center line 730 of the strut 726. This causes the side loading force F.sub.4 of the spring 728 to be directed relatively outboard of the outboard ends 720 of the lateral link pair 718. Although this type of configuration does help to reduce the side loading forces F.sub.4 that are exerted on struts 726 to a point wherein existing struts can handle the side loading force F.sub.4, it does have a disadvantage. In particular, the configuration shown in FIG. 15 adversely affects the designer's flexibility when designing a suspension system. One difficulty with the suspension system of FIG. 15 is its height, which is necessitated by the length of the prior art strut. As will be noted, the spring 728 is placed high, and is disposed generally outside the circumference of the tire. The suspension geometry shown in FIG. 15 is used today because of the inability of presently known struts to handle the side loading forces F.sub.2 that would be imposed by a suspension geometry configuration similar to that shown in FIG. 13.
The suspension system shown in FIG. 14 is conceptually similar to that shown in FIG. 15, in so far as the center line 632 of the spring 628 is offset from the center line 730 of the strut 726. However, as it employs the relatively shorter strut of the present invention, it is more compact than the design shown in FIG. 15, thus giving more flexibility to the suspension system designer than the suspension system shown in FIG. 15. Nonetheless, the flexibility inherent in the suspension system 600 of FIG. 14 is less than the flexibility inherent in the design of FIG. 12.
As such, one object of the present invention is to provide a strut which is capable of handling greater side loading forces, so that suspension designers can utilize the suspension geometry similar to that shown in FIG. 13, which gives to the suspension designer, more freedom in positioning the spring 528 and strut 526. This enhanced flexibility gives the designer more options for designing a suspension system that can fit within the existing space provided within the vehicle. As the space available becomes reduced, this flexibility becomes more important.